Radio broadcasting equipment



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, RADIO fi fiflAbCAS'fING EQUIPMENT Filed Aug. 14 Q 1922 s Sheets-Sheet?f7 .2 M" q 0' l Feb. 19 1924.

1,484,087 F. M. RYAN RADIO BROADCASTING EQUIPMENT Filed Aug. 14. 1922 3Sheets-Sheet 5 lnven/an Frana: M I? an A/fy HRMIHRE i Patented Feb. 19,1924.

UNITED STATES PATENT OFFICE.

FRANCIS M. RYAN, OF EAST ORANGE, NEW JERSEY, ASSIG-NOR TO WESTERN ELEC-TRIC COMPANY, INCORPORATED, OF NEW YORK, N. Y., A CORPORATION OF'NEWYORK.

RADIO BROADCASTING EQUIPMENT.

Application filed August 14, 1922. Serial No. 581,613.

To all 10 ham it may concern:

Be it known that I, FnANoIs M. RYAN, a citizen of the United States,residing at East Orange, in the county of Essex, State of New Jersey,have invented certain new and useful Improvements in Radio BroadcastingEquipment, of which the following is a full, clear, concise, and exactdescription.

This invention relates to radio telephone broadcasting systems andmethod of operating the same and more particularly to control and signalcircuits for such systems.

In radio telephone broadcasting systems it is customary and practicallynecessary to have the radio apparatus located at a distance from thetelephone transmitter used for translating sound waves into audio frequency electric waves. For this reason, th radio apparatus is usuallylocated in one room which may be designated as the radio room; while thetelephone transmitter is located in a separate room which may be calledthe studio or concert room. 'Some means of intercommunication betweenthe studio and radio room attendants must therefore be provided.

An object of this invention is to provide a simple yet effective meansof intercommunication for this purpose. Another object of the inventionis to provide a control system partially under the control of the radioroom attendant and partially under the control of the studio attendant.Another object is to provide a control system, the several parts ofwhich are so interlocked that they will all function in proper sequence.Still another object is the provision of indicating devices toautomatically indicate various circuit conditions.

In one embodiment of the'invention a radio transmitter adapted tomodulate radio frequency waves in accordance with audio frequency wavesis connected to a radiating system or antenna by means of anelectrically operated antenna switch. Audio frequency waves supplied bya telephone transmitter are amplified in an audio frequency amplifierand impressed upon the radio transmitter. The connection of the audiofrequency amplifier to the radio transmitter is controlled by a relay.One telephone transmitter is located in the studio and another in theradio room, the connection of the one or the other to the audiofrequency amplifier being controlled by a manually operated switch inthe radio room. A second manually operated switch in the radio roomcontrols the antenna switch, the amplifier connecting relay and'a signalor supervisory lamp in the studio designated as radio. A manuallyoperated switch in the studio also controls the amplifier connectingrelay, a signal or supervisory lamp in the radio room designated asstudio broadcast and a second lamp in the studio designated asbroadcast. Another lamp in the radio room designated radio broadcast isunder the control of the transmitter switch. A monitoring loud speakingreceiver may be connected either to the audio frequency input circuit ofthe radio transmitter or toa monitoring radio receiver circuit, but onlyat such times as the telephone transmitter in the radio room is notconnected to the audio frequency amplifier.

The novel features which are considered characteristic of this inventionare set forth with particularity in the appended claims. The inventionitself, however, both as to its organization and method of operationtogether with further objects and advantages thereof will best beunderstood by reference to the following description taken in connectionwith the accompanying drawings in which Fig. l and Fig. 2 taken togetherillustrate one embodiment of the invention, while Fig. 3 illustrates amodification of the control circuits of Figs. 1 and 2.

Referring now to- Fig. 1, the blocks A and B enclosed by dot and dashlines represent respectively apparatus located in a studio and amulti-stage audio frequency amplifier. Referring to Fig. 2, blocks C, D

and E also enclosed by dot and dash lines represent, respectively, theradio transmitter whereby radio frequency waves may be modulated inaccordance with audio frequency waves, an electrically operated antennaswitch for transferring the antenna from the receive to the transmitcondition and vice versa, and control and signal apparatus. Theapparatus shown within blocks B, D, and E are ordinarily located in aroom which may be designated as the radio room. The apparatus shownwithin block C with the exception of the sources of filament heating andplate current is also ordinarily located in the radio room.

A telephone transmitter 4 in the studio A comprising two carbon buttons5 and 6, one on each side of a vibrating diaphragm 7, is connected tothe input circuit of the audio frequency amplifier B through the lowercontacts of transmitter switch 8. A similar transmitter 9 in the radioroom shown within block E may be connected to the input circuit of theamplifier B through the upper contacts of switch 8.

The amplifier located on the amplifier panel B comprises three electrondischarge devices 10, 11, and 12 connected in tandem. Each of thesedevices preferably has an ordinary electron emitting cathode orfilament, an anode or plate and an impedance controlling element orgrid. The filaments of devices 10 and 11 are connected in series andheated by current from battery 13 through a circuit which may be tracedfrom the positive terminals of battery 13, which terminal is alsoconnected to ground, through the filament of device 11, resistance 14,filament of device 10, resistance 15, choke coil 16, and filamentcontrolling rheostat 17 to the negative terminal of battery 13. Filamentof clevice 12 is likewise heated by current from battery 13 through acircuit which may be traced from the positive terminal of battery 13through the filament of device 12, choke coil 18, filament cont-rollingrheostat 19 to the negative terminal of battery 13.

Direct current for the transmitters 4 and 9 is also supplied by battery13 over a circuit which may be traced from the positive terminal ofbattery 13 to the left-hand terminal of resistance 20, conductor 21, tothe diaphragms and carbon buttons of transmitters 4 and 9, lower orupper left-hand and middle blades of transmitter switch 8, dependingupon the position of switch 8, conductors 22 and 23, opposite terminalsof input transformer 24 and right-hand terminal of resistance 20, switch25, choke coil 26, resistance 27 to the negative terminal of battery 13.Resistances 20 and 27 with choke coil 26 serve as a potentiometer tocontrol the current to the transmitters 4 and 9.

Space current for devices 10, 11 and 12 is supplied by battery 28through choke coils 29, 30 and 31 connected in parallel by way ofterminals I and J. In case it is desired to use a higher plate potentialfor device 12 than for devices 10 and 11 resistance 32 is former 24. Theamplitude of the impressed waves is determined by the position of switch34 in conjunction with resistance 35. The output circuit of device 10 iscoupled to the input circuit of device 11 through condenser 36 andpotentiometer 37. The output circuit of device 11 is coupled to theinput circuit of device 12 by means of condenser 38 and potentiometer39. The output terminals of device 12 are coupled to the outputconductors 40 and 41 of the audiofrequency amplifier by condenser 42,output transformer 43 and front contacts of relay 44 (normally open).Negative grid polarizing potential for devices 10 and 11 is furnished bythe potential drop across resistances 15 and 14 respectively due to theflow of filament current through those resistances. Negative gridpotential for device 12 is supplied by battery 45.

The radio transmitting apparatus at C comprises an oscillatorO,avariable impedance device M and a thermionic amplifier L. The oscillator0 includes two electron discharge devices 50, connected in parallel andeach having the usual cathode, anode and impedance control element orgrid. The alternating current output circuit of the devices 50 may betraced from their anodes or plates by way of choke coils 51, 51,condenser 52 and primary winding 53 in parallel, and condenser 54 to thecathodes or filaments. Primary winding 53 is inductively coupled tosecondary winding 55 in cluded serially in the circuit of conductor 56which extends to the antenna 57. The primary winding 58 also includedserially in the antenna circuit is inductively coupled to the secondarywinding 59 and serves to feed back oscillations from the antenna circuitto the alternating current input circuit of devices 50 which includeswinding 59 and capacity element 60 in series. The inductometer winding61 which is mounted rotatably with respect to the other windings of theantenna circuit provides variation in the tuning of the antenna 57 whichserves as a frequency determining circuit for the os cillator O. Thevariable condenser 52 serves to so change the constants of the interiorcircuit as to prevent oscillations therein. This interior circuitcomprises winding 59, condenser 60, condenser 54, elements 52 and 53 inparallel and the inherent capacity between the anodes and controlelements. Condenser 52 therefore serves to prevent the absorption ofpower by interior oscillations. It further serves to improve the powerfactor of the plate current, in a measure compensating for the leakagereactance of the winding 53.

Modulation is accomplished by means of the constant current system fullydisclosed at page 360, Proceedings of American Institute of ElectricalEngineers, volume 38,

No. 3. The variable impedance device M comprises two electron dischargedevices 62 connected in parallel. A generator GB supplies space currentto devices 50 and 62 in parallel over a path including constant currentchoke 63, inductance 64 and switch 109. From the negative terminal ofgenerator GB the space current path may be traced by way of theleft-hand blade of switch 109, resistance 67 and resistance 68 to thecathodes of devices 50 and 62. Connected in shunt across the spacecurrent circuit are capacity elements 69 which in conjunction withseries inductance 64 serve to prevent commutator ripples and otherfluctuations in the voltage of source GB- from affecting the spacecurrent, and also serve to prevent high frequency oscillations frombeing impressed upon the generator GB through the space current circuit.In series with the anodes of devices 62 are high frequency choke coils87. The choke coils 51, 51 and 87, 87 prevent parasitic oscillations inthe devices with which they are associated at a frequency above thegenerated radio frequency. Filament heating current is supplied bygenerator GA through switch 110.

The input circuit of thermionic amplifier L is coupled by transformer 73 to the audiofrequency conductors 40 and 41. The secondary winding oftransformer 73 is shunted by resistance 74 to improve the impedancecharacteristic of the transformer 73 in well-known manner. Amplifier Lis supplied with cathode heating current from source GA and with spacecurrent by source GB over a path identical with that of devices 50 and62 except that instead of passing through the constant current choke 63,the space current for the amplifier traverses a resistance 75 to reducethe effective voltage impressed across the electrodes of the amplifier.Resistance 75 is shunted by a capacity element 76 to reduce theimpedance of the output circuit of the amplifier for the amplifiedaudio-frequency current. The transformer 77 couples the output circuitof amplifier L with the input circuit of variable impedance device M. Aresistance 78 of small magnitude with respect to the internal inputimpedance of device 62 is included in shunt with the secondary windingof transformer 77 to stabilize the impedance connected to this winding.The radio frequency choke 79 which freely passes low frequency signalcurrent serves to prevent radio frequency oscillations from beingimpressed upon and dissipated in the circuits of the variable impedancedevice M and the space current generator GB. The cathode of eachelectron discharge device is equipped with an individual regulatingresistance 80 for varying the heating current.

The input circuit of amplifier L may be traced from the impedancecontrol element of the amplifier through the secondary Winding oftransformer 73 to the lower terminal of resistance 67 and thence throughthis resistance and the resistance 68 to the oathode. Since spacecurrent passes through resistances 67 and 68 there will be a potentialdrop between the cathode and the lower terminal of resistance 67, andthe control element or grid of the amplifier L will accordingly bemaintained at a potential negative with respect to that of its cathode.The input circuit of discharge devices 62 is also connected to the lowerterminal of resistance 67 and their impedance control elements areaccordingly maintained at a potential also negative with respect to thecathodes. The grid leak path of the oscillator includes a resistanceelement 81 connected to the upper terminal of resistance 67 and thecontrol elements or grids of the oscillator O are maintained at a lessnegative potential determined by the potential drop across resistance 68in consequence of the space current flowing therethrough. The grids ofthe amplifier L, variable impedance -device M and oscillator O areaccordingly each maintained at such negative potentials with respect totheir individual cathodes as to reduce their respective space currentsto extremely small values. Oscillations are not produced under theseconditions. A time limit relay 82 is connected across the terminals ofgenerator GA. This relay, when energized, closes its normally opencontacts 83 to short-circuit resistance 68, provided antenna switch isin the transmit position and the normally open contacts 84 are closed,as will be described hereinafter. As soon as resistance 68 isshortcircuited the grids of the various discharge devices become lessnegative and permit more space current to flow, thus rendering each ofthe devices operative and causing radio frequency oscillations to beproduced in the antenna. This action is further increased by thereduction of the external resistance in the space current circuit whenresistance 68 is short-circuited, in effect, increasing the effectivespace current voltage. In order to prevent surges in the space currentcircuit in consequence of the opening or closing of contacts 83, a pathincluding a resistance 85 and a capacity element 86 in series therewithis shunted across the terminals of resistance 68.

Ammeters 200 and 201 are conveniently located to measure the spacecurrent of the variable impedance device M and oscillator 0respectively. The unidirectional grid current of the oscillator O andthe antenna current are indicated by ammeters 203 and 202 respectively.

The antenna 57 is normally connected to a radio receiver indicated byblock 87 and erartsin telephone receivers 88 located near the controlapparatus at E through the upper closed contacts 89 and 90 of theantenna switch D. In order to connect the antenna 57 with the radiotransmit-ting apparatus by way of conductor 56, the switch 91 is closed.The closure of switch 91 causes current to flow through relay 92 frombattery 13 to close the normally open front contacts of relay 92. Theclosure of the front contact of relay 92 causes current from the lowvolt age generator GA to flow through the windings 93 of the antenna.relay in parallel. The energization of windings 93 of the antenna relayopens the upper contacts 89 and 90 and closes the lower contacts 94 and95. At the same time normally open contact 84 is closed in order tocomplete the circuit for short-circuiting resistance 68 upon the closureof contacts 83 of time limit relay 82 for the purpose hereinbeforedescribed. A resistance 96 is connected in series with the parallelconnection of windings 93 and when the short-circuit thereabout isremoved by the opening of contact 97 the holding current throughwindings 93 is reduced.

In order that the radio operator may monitor the audio frequency waveswhich are impressed upon the input circuit of the radio transmittingapparatus through transformer 73 the loud speaking receiver 98 isbridged across the input conductors 40 and 41. This receiven may bedisconnected in any suitable manner as circumstances may require.

The closure of switch 91 also causes lamp 100 in the studio A to belighted from the battery 13 and partially prepares a circuit for theenergization of relay 44 from the same battery. If the transmitterswitch 8 is in the lower closed position, the energization circuit forrelay 44 may be traced from the negative terminal of batter 13, switch91, winding of relay 44, right-liand lower closed contact of switch 8,radio broadcast lamp 101, winding of relay 102, switch 103 (it closed)to the positive grounded terminal of battery 13. If the transmitterswitch 8 is in its upper closed position, the energization circuit forrelay 44 instead of extending through lamp 101, relay 102, the switch103 extends through the upper right-hand closed contact of switch 8,resistance 104, switch 105, through ground to the positive terminal ofbattery 13. It is thus seen that audiofrequency waves from the outputcircuit of amplifier B can only be impressed upon the audio-frequencyinput circuit of radio transmitter C through conductors 40 and 41, afterthe switch 91 has been closed and the radio transmitting apparatus isconsequently functioning and connected to the antenna 57. If thetransmitter switch 8 is in the lower position, thereby connecting thestudio transmitter 4 to the input circuit of the amplifier B, the studioattendant has control of relay 44 at switch 103. When switch 103 isclosed, thereby energizing relay 44, the radio attendant is notified bythe lighting of lamp 101 and relay 102 is energized to light thebroadcast lamp 106 in the studio by current from battery 13 through thefront contact of relay 102. A buzzer 107 controlled by push button 108is operated by current from battery 13.

The method of operation is as follows:

Preparatory to operating the system the radio attendant closes radiotransmitter filament heating circuit switch 110, radio transmitter spacecurrent switch 109, audio frequency transmitter switch 25, the filamentheating circuits of amplifier B at variable resistances 17 and 19, whichfor maximum value of resistance may be open circuited, and the spacecurrent circuits of amplifier B at terminals H, I, J and K. Upon theclosure of switches 110 and 109 the generator GA will supply heatingcurrent tothe cathodes of each of the electric discharge devices of theradio transmitter and energizing current to the time limit relay 82, andgenerator GrB will supply space current through resistances 67 and 68 toeach of those devices. After suflicient time has elapsed to permit thecathodes to become fully heated, time limit relay 82 operates to closecontacts 83 preparatory to short-circuiting resistance 68, whenevercontact 84 of antenna relay D is closed.

For reception the radio receiver 87 is used in well known manner.

For transmission the switch 91 is closed operating relay 92. In turnantenna relay D connects the antenna 57 to the radio transmittingapparatus through contacts 94 and 95 of the antenna switch and conductor56. At the same time contact 84 is closed completing the short circuitabout resistance 68. This decreases the normal negative polarizingpotential on the grids or control elements of the amplifier L anddischarge devices 50 and 62 and permits full magnitude space current toflow through each of these devices. The oscillator thereupon producesradio frequency oscillations in the antenna 57. The radio lamp 100automatically lights to indicate to the studio attendant that theapparatus in the radio room is ready to function.

For transmission from the studio, transmitter switch 8 is thrown to itslower closed position. The studio attendant now has complete control ofthe broadcasting equipment, and, when it is desired to transmit, switch103 is closed. Thereupon studio broadcast lamp 101 in the radio roomlights up to indicate to the radio attendant that the studio isbroadcasting and broadcast ace. HMUIMNE QNERQY.

lamp 106 in the studio lights up to warn persons in the studio thatsounds originating therein will be broadcasted.

Sound waves originating in the studio A are impressed upon thetransmitter 4 and the audio-frequency power delivered by the transmitteris in turn impressed upon the amplifier B through the transmitter switch8, conductors 21, 22 and 23 and the input transformer 24. This power isamplified by means of the electron discharge devices 10, 11 and 12 andthe amplified power is then impressed upon the input transformer 73 ofthe radio transmitter at C by means of the closed front contacts ofrelay 44 and conductors 40 and 41.

If it is desired to broadcast by means of the radio room transmitter 9instead of the studio transmitter 4, the transmitter switch 8 is thrownto its upper position, in which case, the broadcasting equipment isunder the control of the radio attendant at switch 105 instead of underthe control of the studio attendant at switch 103.

The modified arrangement of control cir cuits of Fig. 3 will now bedescribed. These circuits are to be considered in conjunction withamplifier B of Fig. 1 and radio transmitter C, and antenna switch D ofFig. 2 to form a complete system. The same reference characters are usedthroughout the drawing to designate the same elements.

The triple-pole double-throw transmitter switch 8 of Fig. 2 is replacedby the two position key 153 at Fig. 3. When the transmitter key 153 isthrown to its lower position the transmitter 4 in the studio isconnected to the input of the amplifier B by means of conductors 21, 22and 23. When the transmitter key 153 is thrown to its upper position theradio room transmitter 9 is connected to the input of the amplifier Bover conductors 21, 22 and 23. Radio lamp 100 in studio A is lighted bythe closure of switch 91 only during such time as transmitter key 153 isthrown to its lower position. Thus, the radio lamp 100 can only belighted when the circuit is completed for broadcasting from the studio.A radio broadcast lamp 154 is lighted when the transmitter key 153 isthrown to its upper position and the circuit is in condition forbroadcasting from the radio room by means of transmitter 9. The lightingof radio broadcast lamp 154 gives warning to any one in the radio roomthat sound waves originating therein will be broadcasted.

A loud speaking receiver 98, provided for monitoring purposes, may beconnected by means of two position key 155 either to the audio frequencyinput circuit of the radio transmitter by way of conductors 151 when thekey 155 is thrown to its upper position or to a monitoring radioreceiver 156 when the key 155 is thrown to its lower position. Themonitoring receiver 98 is automatically disconnected from conductors 40and 41, when the key 153 is thrown to its upper position fortransmitting from the radio room. The loud speaker is so disconnected inorder to prevent singing by retransmission of received sound. Formonitoring on the audio frequency input circuit of the radiotransmitter, when the key 153 is thrown to its lower position forbroadcasting from the studio, the key 155 is thrown to its upperposition. The circuit for the monitorin loud speaking receiver 98 may betraced from conductors 40 and 41 extending between the amplifier B andthe radio transmitter C, conductors 151, closed upper contacts of key155 (normally open), conductors 160, the two left-hand closed uppercontacts of key 153 to monitoring loud speaking receiver 98. Forlistening on the monitoring radio receiver 156, key 155 is thrown to itslower position and the circuit may be traced from monitoring radioreceiver 156, closed lower contacts of key 155 (normallyv open),conductors 160, the two left-hand closed upper contacts of key 153 tothe loud speaking receiver 98. The resistance 161 replaces the radiofrequency receiver 98 across the conductors 151 when the key 155 iseither in the neutral position or thrown to its lower position forconnecting the loud speaking receiver 98 to the monitoring radioreceiver 156.

Double contact relay 162 replaces the single contact relay 102 of Fig.2. When the key 153 is thrown to its lower position for broadcastingfrom the studio, relay 162 is energized over the same kind of a circuitas previously described for relay 102 and which may be traced from thenegative terminal of battery 13, switch 91, winding of relay 44 by wayof conductors 150, right-hand lower closed contact of key 153, windingof relay 162, switch 103, conductor 163, to the positive terminal ofbattery 13. The opera tion of relay 162 causes studio broadcast lamp 101in the radio room and broadcast lamp 106 in the studio to light. Theresist ance 164 is employed to compensate for unequal voltagerequirements of lamp 101 and 106.

For intercommunication between the studie and the radio room, handtelephone sets 170 and 171 are provided. Current for each of these setsis supplied from battery 13 over a circuit which may be traced from thenegative terminal of battery 13, upper winding of retardation coil 172,hand sets 170 and 171 in parallel, provided the push button contacts areclosed, lower winding of retardation coil 172, to the positive terminalof battery 13. Call lamps 173 and 174 are provided respectively in thestudio and the radio room. Lamp 173 is lighted by means of push button175 in the radio room and lamp 174 is lighted by push button 176 in thestudio. In parallel with the lamp 173 is a buzzer 177, the circuit ofwhich is controlled by switch 178. Likewise connected in parallel withthe lamp 174 is a buzzer 179, the circuit of which may be closed byswitch 180. Current for operating both the lamps 173 and 174 and thebuzzers 177 and 179 is obtained from battery 13.

The method of operating the broadcasting system employing the controlcircuits of Fig. 3 is quite similar to the method followed when usingthe control circuits of Figs. 1 and 2. WVhen the switch 91 is closed,placing the radio apparatus in condition for transmitting and when thetransmitting key 153 is thrown to its lower position for broadcastingfrom the studio, the radio lamp 100 is lighted, indicating to the studioattendant that all is in readiness for broadcasting from the studio.When the switch 103 is closed by the studio attendant the amplifier B isconnected to the radio transmitter C by relay 4:4: and broadcast lamp106 in the studio and studio broadcast lamp 101 in the radio room areeach lighted respectively to warn persons in the studio that soundsoriginating therein Wlll be broadcasted and to indicate to the radioattendant that the apparatus is in condition for broadcasting from thestudio. The radio attendant, by means of loud speaking receiver 98 canmonitor the audio-frequency waves impressed upon the radio transmitterby throwing key 155 to the upper position or the radiated energy of theradio transmitter by means of the monitoring radio receiver by throwingkey 155 to its lower position.

For broadcasting from the radio room the transmitter key 153 is thrownto its upper position in which case radio broadcast lamp 154 is lightedto warn persons in the radio room that sounds originating therein willbe broadcasted. Simultaneously, monitoring loud speaking receiver 98 isdisconnected to prevent singing.

From the foregoing description it is seen that a radio broadcastingsystem has been provided in which both the audio-frequency apparatus,radio frequency apparatus and supervisory signals are so interconnectedthat the apparatus will be operated in proper sequence and that theattendants in both the studio and radio rooms will be continuouslyadvised of the circuit conditions of the apparatus. While the inventionhas been described in connection with two of its embodiments, it will beobvious to those skilled in the art that other modifications of by theaccompanying claims.

What is claimed is:

1. The method of operatinga radio telephone broadcasting system whichcomprises producing audio frequency electric waves by means of soundwaves, producing radio frequency waves, radiating said radio waves andautomatically preventing an attempt to modulate said radio waves withsaid audio frequency waves except during such time as said radio wavesare being radiated.

2. In a radio telephone broadcasting system, having a radio room and astudio, the method of operatin said system which comprises producing ani0 frequency waves by means of sound waves in said studio, producingradio frequency waves in said radio room, radiating said radio waves,automatically preventing an attempt to modulate said radio waves withsaid audio frequency waves except when said radio waves are beingradiated and automatically indicating to the studio that radio waves arebeing radiated.

3. I11 a radio telephone broadcasting system, an antenna, a radiotransmitter for modulating radio frequency power in accordance withaudio frequency power, a source of audio frequency power, means toconnect said radio transmitter to said antenna, and means effective onlywhen said radio transmitter is connected to said antenna to connect saidsource of audio frequenqy power to said radio transmitter.

4. n a radio telephone broadcasting system, a radio room and a studio, aradiating system, a source of audio frequency waves located in saidstudio, a radio transmitter whereby radio waves are modulated inaccordance with audio frequency waves, means for impressing said radiofrequency waves upon said radiating system, a second means forimpressing said audio frequency waves upon said radio transmitter, athird means in said studio effective upon the operation of'said secondmeans to impress audio fre quency waves upon said radio transmitterproviding said first mentioned means has been actuated to cause radiofrequency waves to be impressed upon said radiating system.

5. In a radio telephone broadcasting system, a radio transmitter wherebyradio waves may be modulated by audio frequency waves, a first source ofaudio frequency waves, a second source of audio frequency waves locatedat a distance from said first source and said radio transmitter, meansto connect either said sources separately to said radio transmitter andan indicating device for said first source automatically operated by theconnection of said second source to said radio transmitter.

6. In a radio broadcasting system, a radio transmitter for modulatingradio frequency 25o, aao aar scissor,

waves in accordance with audio frequency waves, an antenna, an antennaswitch for connecting said radio transmitter to said antenna, an audiofrequency amplifier, a relay for connecting said amplifier to said radiotransmitter, a source of audio frequency waves, a manually operatedswitch for connecting said audio frequency source to said audiofrequency amplifier, a switch near said audio frequenc source forcontrolling the operation of said relay, an indicating device near saidaudio frequency source to automatically indicate both that the radiotransmitter is connected to the antenna and that the audio frequencysource is connected to said audio frequency amplifier and a secondindicating device near said first device and a third indicating devicenear said audio frequency amplifier, said second and third devices beingautomatically actuated when said relay is actuated.

7. In a radio broadcasting system, a radio transmitter for modulatingradio power in accordance with audio frequency power, a radio frequencypower output circuit and an audio frequency power input circuit for saidradio transmitter, an antenna, an electrically operated antenna switchfor conmeeting said radio output circuit to said antenna, a source ofaudio frequency power, a relay for connecting said audio frequencysource to said radio input circuit, a switch for controlling theoperation of said relay, and a second switch controlling the operationof both said antenna switch and said relay.

8. In a radio telephone broadcasting system, a studio, a radio room,means in the radio room for radiating radio frequency power, means toindicate to the studio that radio frequency power is being radiated,means in the studio for furnishing audio frequency power for modulatingsaid radio frequency power, and means in the radio room for indicatingwhen said last mentioned means in the studio is ready to function.

9. In a broadcasting station, a studio, a radio room, means whereby aperson in either room may broadcast, and means in each room toautomatically indicate that the circuits are in operating condition forbroadcasting from that particular room.

10. In a broadcasting station, a radio room, means therein forcontrolling the operation of a radio transmission system, a studio,means in said studio for automatically indicating if said radio systemis in transmitting condition, and means in said radio room to indicatethat someone in the studio is ready to broadcast.

11. In a broadcasting station, a radio room, means therein forcontrolling the operation of a radio transmission system, a studio,means in said studio for automatically indicating if said radio systemis in transmitting condition, and means in said radio room forautomatically indicating that someone in the studio is ready tobroadcast.

12. In a broadcasting station, a radio room, radio transmittingapparatus located therein, a studio, and means for automaticallyindicating in said studio that said radio apparatus is in transmittingcondition.

13. In a radio telephone broadcasting system having a radio room and astudio, a method of operating said system which comprises producingaudio frequency waves in said radio room and automatically indicating tothev studio that radio waves are being produced.

14. In a broadcasting station, a radio room, a studio, means in bothsaid rooms for jointly controlling the operation of a radio transmissionsystem, and means for automatically indicating in either room thecondition of the control apparatus in the other room. I

In witness whereof, I hereunto subscribe my name this 11th day of AugustA. D.,

FRANCIS M. RYAN.

